This invention relates to fusing machines, and more particularly, to machines for fusing the armature wires of an electric motor, and the application and control of electric current to generate heat during the fusing operations.
Fusing machines are widely used for fusing armature wires to commutators, and stator wires to terminal boards, of electric motors. Commutators typically have tangs or slots to which the wires are attached. Terminal boards typically have contact hooks for wire attachment. A typical armature fusing operation involves applying a physical force from the fusing electrode to the tang or slot being fused. Next, current is applied to the fusing electrode, which passes through the commutator to a ground electrode. The resistance of the fusing electrode is higher than that of the commutator, causing the fusing electrode to heat. The heat is thermally transferred to the point of contact between the fusing electrode and the commutator. Additional physical force may be used, as well as additional applications of current, to complete the fusing operation. A similar set of steps is required for stator fusing operations.
Precise control of the physical and electrical phases of the fusing operation has been difficult to achieve. U.S. Pat. No. 5,063,279 describes a fusing machine having precise control of the physical phases of the fusing operation. The application of force from the fusing electrode to the commutator bar (or terminal board) and wires is performed according to predetermined force or displacement functions. This provides a fusing machine that continuously monitors electrode force or displacement and provides rapid feedback for maintaining a precise application of force throughout the fusing operation.
Precise control of the electrical phases of fusing operations has yet to be achieved. The lack of precise control of the application of current during fusing can cause unintentional significant heating to occur (such as throughout the commutator bar). The production of modern commutator cores includes materials that are more sensitive to heat than previous materials (e.g., asbestos). The structural characteristics of these modern cores may be altered by uncontrolled significant heating, thereby causing impairment of the core materials' ability to anchor the commutator bars. This might result in, for example, the commutator bars coming loose from centrifugal force during normal operation of the motor. Similar advantages exist with stator terminal boards due to the use of extremely variable metal alloys in terminal board construction.
The quality of the fused joint is also affected by the level of precision used in the application of current during fusing. The heat generated by the fusing electrode provides two main purposes. First, the applied heat causes a plastic deformation to occur to the parts being fused without their temperature reaching a molten state (unlike welding). Second, the applied heat is used to vaporize the insulation of the wire being connected to the commutator (or terminal board). This vaporization is critical to the efficient production of motor windings. When sufficient heat is not generated in a precise manner, there is not consistent and complete removal of insulation from the wire. Additionally, the imprecise application of heat during tang fusing can result in unreliable cohesion joints between the commutator and the wire.
In an effort to try to achieve high quality fusing, time consuming and complex operations must be undertaken to set up the fusing machine. Such operations could be avoided if a fusing machine could precisely apply various levels of current at the proper time throughout the fusing operation. Additionally, a more precise delivery of heat during fusing would result in an overall reduction in heat required and a saving of energy consumed during the overall fusing operation.
Conventional systems exist which supply current in the form of impulses which are derived from a normal sinusoidal alternating current (AC) supply line. One such invention is described in U.S. Pat. No. 4,001,539, which describes a control system that supplies electric current to welding electrodes. This system is based on supplying a series of current pulses, which represent slices of the sinusoidal input signal, as a series of output pulses. Current amplitude is varied by affecting a phase shift as to when, and for how long, the output pulses are supplied to the welding electrode.
Current delivery by pulsing requires that relatively long pauses occur between the delivery of each output pulse while waiting for the input signal to reach the desired amplitude or phase again. The long pauses are impractical when attempting to achieve precise control of the delivery of current during fusing operations. Further, the long pauses prevent synchronization between complex physical phase profiles and electrical supply profiles because typical regulating supplies can not keep pace with the rapid changes in current requirements. In addition, the long pauses require that the applied current be delivered at higher levels than would be necessary if the current were applied continuously in order to achieve proper heating. The higher current causes accelerated deterioration of the electrode (cratering, where holes form in the electrode surface), thereby reducing the life of the electrode.
It would therefore be desirable to provide a fusing machine which applies electric current in a manner which is consistent with the time of any variation during fusing operations. It would also be desirable to provide a fusing machine which limits significant heating to only the parts which form the fused joint. It would also be desirable to provide a fusing machine which provides consistent and complete removal of wire insulation, and in the case of tang fusing, a more reliable cohesion joint. It would also be desirable to provide a fusing machine which does not require complex and time consuming set-up operations to achieve high quality fusing. It would also be desirable to provide a fusing machine that requires less heating and energy to perform fusing operations. It would also be desirable to provide a fusing machine which provides current delivery in such manner that reduces electrode deterioration.